Main circuit breaker



FIG. 1 is a perspective view of a main circuit breaker showing our new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a right end elevational view thereof;

FIG. 6 is a front elevational view thereof;

FIG. 7 is a left end elevational view thereof. 

The ornamental design for a main circuit breaker, as shown and described. 